Microdialysis Calibration Research Articles

A Review on Microdialysis Calibration Methods: the Theory and Current Related Efforts.

Microdialysis is a sampling technique first introduced in the late 1950s. Although this technique was originally designed to study endogenous compounds in animal brain, it is later modified to be used in other organs. Additionally, microdialysis is not only able to collect unbound concentration of compounds from tissue sites; this technique can also be used to deliver exogenous compounds to a designated area. Due to its versatility, microdialysis technique is widely employed in a number of areas, including biomedical research. However, for most in vivo studies, the concentration of substance obtained directly from the microdialysis technique does not accurately describe the concentration of the substance on-site. In order to relate the results collected from microdialysis to the actual in vivo condition, a calibration method is required. To date, various microdialysis calibration methods have been reported, with each method being capable to provide valuable insights of the technique itself and its applications. This paper aims to provide a critical review on various calibration methods used in microdialysis applications, inclusive of a detailed description of the microdialysis technique itself to start with. It is expected that this article shall review in detail, the various calibration methods employed, present examples of work related to each calibration method including clinical efforts, plus the advantages and disadvantages of each of the methods.

An in Vitro Hydroxyl Radical Generation Assay for Microdialysis Sampling Calibration

A xanthine oxidase hydroxyl radical (·OH)-generating system was created for sustained in vitro production of ·OH. This assay was coupled with microdialysis sampling to elucidate the factors that influence microdialysis calibration during radical trapping. A ·OH trapping agent, 4-hydroxybenzoic acid, was included either in the microdialysis perfusion fluid or in the medium external to the microdialysis probe. Xanthine oxidase enzymatic activity was reproducible and had an average activity measured by UV absorbance of produced uric acid of 0.037 ± 0.005 ΔAU/min (n = 5). A considerable amount of variance in the rate and amount of the product, 3,4-dihydroxybenzoic acid (3,4-DHBA), was observed when one microdialysis probe was placed in the reaction mixture. When two microdialysis probes were placed in the reaction mixture, a greater rate and amount of 3,4-DHBA was observed. Different concentrations of 3,4-DHBA were obtained between quiescent and stirred systems.

Quantification of ethanol concentrations in the extracellular fluid of the rat brain: in vivo calibration of microdialysis probes.

Traditional microdialysis techniques provide qualitative data, although quantitative data are often required for pharmacodynamic analyses. This study evaluated a potentially useful in vivo delivery technique to calibrate microdialysis probes for ethanol. We measured in vivo delivery extraction fractions within subjects across 2 days and found no change over time. We tested the effect of diffusion direction on extraction fraction and found that it was higher for ethanol diffusion out of the probe than for diffusion into the probe, both in vitro and in vivo. The in vivo extraction fraction ratio of diffusion(IN) versus diffusion(OUT) was 0.65+/-0.03. Finally, we predicted extracellular brain ethanol concentrations after 1 g/kg ethanol administration using in vivo delivery, "no net flux" dialysis, or in vivo delivery corrected for diffusion direction with the in vivo extraction fraction ratio. Both in vivo delivery and "no net flux" dialysis predicted brain concentrations that were approximately one-third lower than blood concentrations, whereas the corrected in vivo delivery predicted extracellular concentrations very similar to blood concentrations. We conclude that microdialysis calibration methods for ethanol require a measure of extraction fraction for diffusion into the probe. Further studies are needed to establish whether this effect is common to other alcohols.

Validation of the internal reference technique for microdialysis measurements of interstitial histamine in the rat

The internal reference technique (IRT) was compared with the no net flux method (NFM) as a microdialysis calibration technique for sampling of interstitial histamine in the rat. Microdialysis catheters (polyacrylonitrile, 50 kD cut off) were inserted in liver, muscle, subcutaneous tissue and in an induced adenocarcinoma. Estimated relative recovery with IRT ranged from 23 ± 2% in liver to 30 ± 3% in subcutaneous tissue with and without tumor (p < 0.05). By using the NFM-technique we found similar recovery as compared to the IRT in all tissues studied. Interstitial histamine was up to 3-fold higher than the mean plasma histamine concentration (54 ± 2 nmol/l). Subcutaneous tissue (177 ± 39 nmol/l) and subcutaneous tumor (165 ± 29 nmol/l) exhibited high histamine while liver (65 ± 14 nmol/l) and liver tumor (75 ± 7 nmol/l) had low interstitial histamine concentrations. In conclusion, the IRT was validated against the NFM as a rapid method for histamine measurements in situ in the rat.

Methods and issues in microdialysis calibration

A review of calibration in microdialysis is presented. This review covers the methodological aspects of microdialysis including how physico-chemical parameters such as analyte diffusion coefficient, kinetics, volumetric flow rates, and membrane length affect calibration. The effects of diffusion versus diffusion coupled with chemical reaction are discussed in relationship to microdialysis extraction fraction and calibration. Resistance theory is used throughout to illustrate how diffusion and chemical reaction affect microdialysis calibration. In vivo calibration methods such as mass transfer coefficient, no-net flux method (Lönnroth method), internal standards (retrodialysis), in vivo delivery, and slow perfusion method are discussed. Applications of these various in vivo calibration methods are also included. Mathematical models are presented as a means to help understand the physical parameters that affect microdialysis calibration. Finally, the challenges in interpreting results from transient methods such as trapping free radicals and in situ metabolism are discussed.

In vitro and in vivo microdialysis calibration using retrodialysis for the study of the cerebrospinal distribution of bupivacaine

Microdialysis coupled to HPLC was used to study the disposition of local anesthetics in the cerebrospinal fluid (CSF) because of the difficulty in sampling CSF. A retrodialysis method for the microdialysis calibration was investigated in vitro and in vivo. Calibration by retrodialysis was simultaneously validated through the use of the zero net flux method. Two local anesthetics (bupivacaine and ropivacaine), which differ structurally by only one methyl group, were respectively utilized as substance of interest and as internal standard. Different parameters were tested in vitro to compare the relative recovery ( RR) of bupivacaine and the relative loss ( RL) of ropivacaine. Several flow rates were tried to select an optimal in vivo flow rate (1 μl/min). The RR and RL values were not influenced by the variation of bupivacaine concentration. A significant variability among different probes within a batch was established ( RR ranging from 41.1–65.3%; RL ranging from 30.7–61.0%). The K-factor values, defined as RL ropivacaine/ RL bupivacaine, were calculated in vitro and in vivo. This ratio decreased in vivo but was constant ( K in vitro=1.06±0.04, K in vivo=0.87±0.03). The extracellular tissue concentration of the compound of interest was given by C= C in dialysate×( K/ RL). Following in vivo implantation in rabbit CSF during 4 h, the probes were tested again in vitro and no deterioration of probe during the in vivo experiment was found. After administration of bupivacaine in the epidural space of rabbits, plasma and microdialysis CSF samples were simultaneously collected. Plasma and CSF disposition of bupivacaine displayed different kinetics. The maximum CSF concentration of B averaged 394±170 μg ml −1, with a mean T max of 3.8±1.8 min. The maximum plasma concentration of B averaged 0.44±0.09 μg ml −1 with a mean T max occurring at 1 min. Microdialysis, combined with accurate calibration, should be a reliable technique to gain further insight in the spinal disposition of local anesthetics.

Microdialysis calibration using retrodialysis for the measurement of local anaesthetics in rabit in rabbit cerebrospinal fluid

Microdialysis calibration using retrodialysis for the measurement of local anaesthetics in rabit in rabbit cerebrospinal fluid

Key metabolite kinetics in human skeletal muscle during ischaemia and reperfusion: measurement by microdialysis.

The tissue kinetics of key metabolites of ischaemic and postischaemic tissue damage were studied in the intercellular space of human skeletal muscle by microdialysis. In vivo microdialysis calibration experiments (n = 5) yielded the basal intercellular concentration of glucose in human skeletal muscle (3.6 +/- 0.6 mM; mean +/- SD). The corresponding mean plasma glucose concentration was 4.3 +/- 0.2 mM which was significantly higher. The time vs. concentration profiles of intercellular glucose (n = 7), lactate (n = 5), TxB2 (n = 6) and urea (n = 8) were characterized during a 20 min period of leg constriction. TxB2 increased exclusively during reperfusion in comparison to baseline (n = 6). Administration of 500 mg acetylsalicylic acid, 5-10 min after onset of ischaemia blunted TxB2-response to reperfusion (n = 4). It is concluded that intercellular muscle glucose concentration is less than that in plasma. Glucose uptake in skeletal muscle is rapid even under ischaemic conditions. Synthesis and release of TxB2 is not evident during ischaemia. TxB2 mediated reperfusion injury might be reduced by acetylsalicylic acid, even if administered after onset of ischaemia.

In vitro and in vivo microdialysis calibration for the measurement of carbamazepine and its metabolites in rat brain tissue using the internal reference technique

Microdialysis, as in vivo sampling technique, can be used for determining exogenous compounds in the extracellular fluid of freely moving animals and in humans. Usually, calibration of the microdialysis probe is determined by in vitro relative recovery (RR) (dialysate extraction fraction). However, due to different diffusion properties of the compound in tissue, the RR in vivo is different from the RR in vitro. In this study, the evaluation of the internal reference technique as in vivo calibration method was established. To determine the RR in vivo, the relative loss (RL) was defined as the loss of a compound from the perfusate. RL was determined in vitro and in vivo by adding an internal standard (IS) to the perfusate. This internal reference technique was applied for the determination of carbamazepine (CBZ) and its 2 major metabolites, carbamazepine-10,11-epoxide (CBZ-EPO) and trans-10,11-dihydroxy-10,11-dihydro-carbamazepine (CBZ-DIOL) using 2-methyl-5H-dibenz(b,f)azepine-5-carboxamide (m-CBZ) as IS. In vitro and in vivo, the loss of m-CBZ and the recovery of CBZ are identical. The ratios of the RR of CBZ-EPO and CBZ-DIOL to the RL of m-CBZ are constant, in vitro and in vivo. Therefore, m-CBZ can be used as IS for CBZ, CBZ-EPO and CBZ-DIOL determinations in brain tissue. It is shown that the internal reference technique is a useful method to estimate the true concentration of exogenous compounds in the extracellular space of tissues.

Microdialysis calibration using retrodialysis and zero-net flux: application to a study of the distribution of zidovudine to rabbit cerebrospinal fluid and thalamus.

A retrodialysis (RD) method for the real-time calibration of on-line microdialysis (MD) procedures was investigated in vitro and in vivo. Calibration by retrodialysis was simultaneously validated through the use of a zero-net flux (ZNF) method, which assumes directional independence of diffusion of the solute. In RD, a calibrator with dialysance (PeA; effective permeability-surface area product) similar to that of the compound of interest is introduced into the perfusate. If the calibrator is suitable, its loss from the perfusate during RD is identical to the recovery of the solute of interest determined simultaneously by normal MD. Two antiviral nucleosides (AZT and AZdU) which differ structurally by only a methylene group were utilized as solute and calibrator, respectively. Both nucleosides exhibited similar recovery and loss at flow rates of 0.5 to 5 microL/min in vitro, indicating a similar PeA product in this flow domain. Furthermore, both compounds showed similar loss into the lateral ventricle or thalamus of rabbits (n = 4) during RD at a flow rate of 1 microL/min for 6 hr. The relative loss decreased rapidly within the first hour, reaching a relatively stable value after 2 hr. The significant reduction in the loss of AZdU and AZT in vivo compared with that in vitro likely results from a lower diffusion coefficient in tissue. The distribution of AZT between plasma and cerebrospinal fluid (CSF) in the ventricle and extracellular fluid (ECF) in thalamus was determined at steady state using calibration by RD and ZNF simultaneously.(ABSTRACT TRUNCATED AT 250 WORDS)